With the corrector off, I located the culprits: The nuts that hold on the nice chrome counterweight bars. Criterion painted these with flat black, but over 4 decades, the paint came loose in places. I wiped those down, along with the complete interior, then used my computer vacuum to get any strays. Then, I cleaned the primary mirror. Now, I can look down the tube, and it's clean as a whistle!

I'll say one thing for the DX8: It's very easy to work on. Simple design, common components, and it fits back together without a hitch.

Another thing about my DX8: It ain't no Questar! The corrector is not a perfect circle, and its edges are kinda rough; whereas, my Q's meniscus is as precisely ground & finished as my Telementor's lens. It's like I asked The Boys to make it from an old storm door...

The mirrors are in excellent condition. The coatings are every bit as flawless as the Tinsley's after Majestic worked their majik on them.

IF the scope performs well, I'll think about flocking the interior. For now, I just want to see what it can do as delivered.

BIF: The B&L eyepiece adapter came today. I got it on eBay, part number 63-1013, and it threads on perfectly. It's supposed to fit the DX6, too. Machined aluminum, complementary DX details, and holds 1.25" accessories securely.

If the corrector isn't round then that makes it a problem in finding it's true optical centered so it can be properly aligned. It's also questions if the hole in the middle of it for the secondary is also optically centered or not ? The only way I know to check it is to place it up against an optical flat so you can find the neutral zone of the corrector. Here is a picture of what I mean. You can see were the interference fringes are the strongest and that is the neutral zone of the plate. Hopefully the neutral zone will be perfectly round and then you can measure it's diameter and from that determine the optical center of the plate. Here is also one of Celestron corrector showing the neutral zone as well.

David, virtually nobody has optical flats. You do, but you are not a typical amateur astronomer - not by a long shot.

And, if you find that the plate was cored off-optical center, what are you going to do, re-core the corrector plate? Maybe you could shim the secondary holder off center, but then you have the problem of centering the corrector off it's mechanical center.

I understand your point, and I appreciate your skills. I just can't agree that the methods you discuss here are in the realm of possibility of the general members here.

If a user can refigure a corrector, all the things you discuss are doable. Just realize that it's beyond the ability of most of us.

Actually, before cleaning, the secondary assembly was centered within .1mm; I returned all the bits to their original positions, including the cork shims, and the secondary is again dead center. Also, with the 3 mirror collimation screws loosened, it can move about 1mm in any direction horizontally & vertically. It made nailing collimation tougher than my Tinsley, but Criterion put in enough slack to get the pieces aligned without anything more than a screwdriver. Again, simple design & components. I've done my part. It boils down to the quality of the optics. And, since the skies cleared a day earlier than predicted, I'm going to test those optics tonight -- along with the Big Eye Cee (Carton 101mm monocular).

David, virtually nobody has optical flats. You do, but you are not a typical amateur astronomer - not by a long shot.

And, if you find that the plate was cored off-optical center, what are you going to do, re-core the corrector plate? Maybe you could shim the secondary holder off center, but then you have the problem of centering the corrector off it's mechanical center.

I understand your point, and I appreciate your skills. I just can't agree that the methods you discuss here are in the realm of possibility of the general members here.

If a user can refigure a corrector, all the things you discuss are doable. Just realize that it's beyond the ability of most of us.

Gil,

If your going to do a job you need the right tools to do it and I'm showing people how to do the job with those tools.So what is the alternative then ? Just roll the dice and hope your get it right or use a telescope that doesn't give a good image ? If you have the right equipment many times it is very easy to fix a problem .

You can buy an optical flats at places like Ebay and Surplus Shed for not much money. Rolo got a 12" one for around $120. Here is 1/20 wave at Surplus Shed that would allow one to map out the corrector and find the neutral zone http://www.surplussh...tem/pm1017.html for $20.

If you want your scope to perform especially these vintage ones that who knows what has been done to them, you need to take the time to understand how optics work and how to test them. People here have posted wonderful mechanical restoration jobs and spent a fair amount of time and money doing them, including the tools to do it. People don't think twice on dropping $50 for certain tool to get a job done or buying custom blended paint to match a vintage finish. In most cases the tools needed to test optics are cheaper and it is no harder to test them as it is for some the mechanical work I see people doing.

As for what to do if the optical center doesn't match the mechanical center, you center everything up using the optical center as the reference. If not the scope won't perform. It is the same has have Newtonian out of the collimation or element in a refractor off center.

Personally, although I do not make my own optics, I am excited to hear that there are beginning to be amateurs who can refigure an SCT. We ought to be masters of our tools, at least as a community, if not as individuals.

My indoor collimation was good, but it wasn't great. I tweaked the DX8 on Pollux, then moved to Castor with the OR20, and got two beautiful orange stars. Had to make it a brief work night session, so I went from there to Jupiter, and saw 6 belts at 100x. OR12 @ 176x was very nice. Sharp limb, splitting in the SEB, and mottling browns in both EQ belts. I only gave the DX8 about 30 mins to adjust (while I got wowed by the Carton 101mm monocular). I give the Tinsley at least an hour. I don't think it'll match the Cassegrain in resolution, but I'll be glad to be proven wrong. Right now, I'm just relieved that the planetary images aren't mush!

If you got decent, detailed images at 176X, that is a very good sign and I think you got a good one. My blue DX8 produces mush at anything over 30X, my grey ones perform as yours does.

I can do optical testing at my friend's shop, when he's around (we tested Keith's Tinsley objective a few weeks ago using double-pass autocollimation), but I really need to make room in the basement and set up to do it there. Right now there just isn't room. It's a path only from one spot to another, I need to get my ex-wife to come and get the last of her stuff- it's only been six years. Or maybe I can charge her a storage fee that will offset the alimony? Hmmm....

Y'all should see that huge DX8 balanced on the D&S. Two of its bolt holes aligned with the head's long slot, so I had it secured, but I'm sure the DX8 could've pulled it over! But setup on the lawn is a big advantage over my pedestal mounted scopes. With a proper wedge & tripod, this heavy SCT should be a breeze to use.

Don't know if this is common, but my DX8's focuser feels too slick. I'll have to adjust it if possible, because it slipped going from horizon to zenith. Also, as humid as The Swamp is, it'll have to have a dewshield.

My initial views are pretty typical for an 8" SCT. I think it would've improved some during the next hour. Seeing was a good 8/10, and the Carton was ready in just a few minutes. On nights like this one, my Edmund 4 rules on any object I target, but my Questar requires patience to get its best views. I think the DX8 will be similar.

Will it be a planet killer like my Tinsley? Probably not. But the extra 2" aperture should do well on DSOs. And the DX8 can go to dark sites, which is not practical for the old 6" Cass.

One thing I noticed immediately was that the background sky wasn't black at the zenith, as it is in both the Questar & the Tinsley (and all my long refractors, of course). Also, at 200x the Tinsley shows the 4 Galilean moons as disks, with hints of color on Io. The DX8 doesn't. All four had intermittent / broken rings. But like my other reflectors (and my Goto f/20), Jupiter's disk is a pearly white, which makes the belts jump out. Terra suggested flocking, and I think that'll help with the contrast. I don't think Criterion's black absorbs as well as the chalkboard black.

OTOH, the DX8 should do well imaging DSOs, and I have a camera now that can catch those nebulae & galaxies.

Criterion put a handy alignment mark on the corrector and the inner cell. 4 small cork bits shim the glass, keep it centered, and keep it from contacting the aluminum ring. I marked the locations with a pencil before removing them. As you can see, the corrector & secondary had paint debris, too.

I see that the tradition continues in how telescope manufacturers align and center the corrector plate using cork and strategic placed engravings. My "modern day" manufactured LX200-R/ ACF SCT is assembled similarly.

David, virtually nobody has optical flats. You do, but you are not a typical amateur astronomer - not by a long shot.

And, if you find that the plate was cored off-optical center, what are you going to do, re-core the corrector plate? Maybe you could shim the secondary holder off center, but then you have the problem of centering the corrector off it's mechanical center.

I understand your point, and I appreciate your skills. I just can't agree that the methods you discuss here are in the realm of possibility of the general members here.

If a user can refigure a corrector, all the things you discuss are doable. Just realize that it's beyond the ability of most of us.

Gil,

If your going to do a job you need the right tools to do it and I'm showing people how to do the job with those tools.So what is the alternative then ? Just roll the dice and hope your get it right or use a telescope that doesn't give a good image ? If you have the right equipment many times it is very easy to fix a problem .

You can buy an optical flats at places like Ebay and Surplus Shed for not much money. Rolo got a 12" one for around $120. Here is 1/20 wave at Surplus Shed that would allow one to map out the corrector and find the neutral zone http://www.surplussh...tem/pm1017.html for $20.

If you want your scope to perform especially these vintage ones that who knows what has been done to them, you need to take the time to understand how optics work and how to test them. People here have posted wonderful mechanical restoration jobs and spent a fair amount of time and money doing them, including the tools to do it. People don't think twice on dropping $50 for certain tool to get a job done or buying custom blended paint to match a vintage finish. In most cases the tools needed to test optics are cheaper and it is no harder to test them as it is for some the mechanical work I see people doing.

As for what to do if the optical center doesn't match the mechanical center, you center everything up using the optical center as the reference. If not the scope won't perform. It is the same has have Newtonian out of the collimation or element in a refractor off center.

- Dave

"People don't think twice on dropping $50 for certain tool to get a job done or buying custom blended paint to match a vintage finish. In most cases the tools needed to test optics are cheaper and it is no harder to test them as it is for some the mechanical work I see people doing."

This is an interesting point from Dave. Sadly, not many people go for a scientific test to determine optical quality; instead, it's the eyeball factor. The best determination for the given quality of an optic set is to put it on the bench.

Have you given any thought to the resale value of a Dynamax 8 with known good optics and in good condition? I can't afford to add such a thing to my collection right now, but there must be others who would jump on it!

Have you given any thought to the resale value of a Dynamax 8 with known good optics and in good condition?

No, not really. I don't buy vintage scopes as an investment, though I do want my heirs to get their money's worth once I'm gone. That's why I wrote up a descriptive inventory with my estimates of market & auction prices -- plus the lowest amount I would take for a given scope.

The issue I keep experiencing is that most commercial telescopes have optics that are in the 1/2 wave or worse range. So a majority of observers are calibrated to the image produced in those telescopes as being "good". My own DX-8 which I have posted images of how the optics tested out on the bench ( very bad) will show me the belts on Jupiter and the craters on the Moon. I watched a transit of the one of Jupiter's moons with it. If I took that scope to a public out reach I'm sure I would get a bunch of OMG's when people looked thru it BUT if I put my DX-8 next to one on my scopes with true 1/8 wave optics you could easily see the difference of what your were missing. Jupiter wouldn't have that "fuss" to it any more and all of sudden all this fine detail in the belts would be easily visible vs blaming the lack of detail in the poor quality scope because of the seeing. or the scope hasn't cooled enough or the eyepiece etc etc.

Just two days ago I tested a custom made mirror that was over 20" in diameter made by a high end mirror maker for a member of my club. He just received it and paid many thousands of dollars for. It had a pretty bad turned edge that owner could easily see as well when we tested it. It didn't require a fancy test equipment to see the defect just a simple Foucault tester that I made when I was a kid for a few dollars. What is just as interesting is the fact the maker of this mirror doesn't provide test data but his only claims that his mirrors will give "good images". Well, define "good". The maker's definition of "good" and owners definition of "good" can be two different things vs the scientific definition of "good'. Also from what I have seen of other commercial mirrors that are much less expensive but known to be of "lesser quality", this mirror is no better.

So if you don't test your optics you can be playing the same game as the old fable of "The Emperor has new Cloths". Just because someone keeps tells you have great optics doesn't mean you do but your wallet will be much lighter.

I really need to make room in the basement and set up to do it there. Right now there just isn't room.

I'm in the same boat; and, we're going to be moving out to get our current home fixed up & sold. So, no BB Optical Test Lab any time soon. Like other serious observers, I have to rely on my memories of observing through different scopes at star parties, and my own set of "reference scopes" - like my Telementor 2, Tinsley 6" Cass, and Edmund 4" refractor.

The T2 would blow the sox off any observer. It's a 63mm that thinks it's a 150mm. I've used much larger Casses than my Tinsley 6, and larger refractors than my Edmund 4.

I'm pretty certain that my DX8 is typical of this class. Good optics, but not great optics. Given the convenience of the form factor, it's an acceptable compromise versus an 8" f/10 refractor! Another classic bargain in my collection, and it will require very little effort to improve & maintain.

The issue I keep experiencing is that most commercial telescopes have optics that are in the 1/2 wave or worse range. So a majority of observers are calibrated to the image produced in those telescopes as being "good". My own DX-8 which I have posted images of how the optics tested out on the bench ( very bad) will show me the belts on Jupiter and the craters on the Moon. I watched a transit of the one of Jupiter's moons with it. If I took that scope to a public out reach I'm sure I would get a bunch of OMG's when people looked thru it BUT if I put my DX-8 next to one on my scopes with true 1/8 wave optics you could easily see the difference of what your were missing. Jupiter wouldn't have that "fuss" to it any more and all of sudden all this fine detail in the belts would be easily visible vs blaming the lack of detail in the poor quality scope because of the seeing. or the scope hasn't cooled enough or the eyepiece etc etc.

I know what you mean. My new Celestron EdgeHD appears to be a "gem," better than 3 previous 8-inch SCTs, even at center of field, where the EdgeHD design should not be appreciably different from conventional SCT. I think I got a good one.

I do majority of my testing on either my kitchen table or kitchen counter tops when it come to finished optics and everything gets put neatly away when I'm done. I also setup two chairs temporarily in my living room, one with the mirror setup on it and the other with the tester on it. So you don't need a permanent setup to do optical testing. Yes I do have a setup in my basement but I used that when I'm figuring optics because once I get everything set up, I can quickly go from the pitch lap, to the test stand and see what is going on with the figure and right back to the pitch lap to continue work.

I made my first mirror as kid in the parent house using the cloth hamper as a stand with a plywood top I made for it. The story goes that Bernard Schmidt was making optics on the top of a chest of drawers in the room he was renting.

My kitchen table is about 4 feet in diamter, and my wife would kill me if I set up even a temporary optical bench there. Ain't gonna happen until I get the basement cleaned out! Of course, I have a friend with a Zygo- not everyone does.

My kitchen table is about 4 feet in diamter, and my wife would kill me if I set up even a temporary optical bench there. Ain't gonna happen until I get the basement cleaned out! Of course, I have a friend with a Zygo- not everyone does.

Four feet is too small for me, I need 10-12' for mirror testing. 4-5' works with most refractors using a flat.

Based on the corrector number (740205) my OTA is the 205th made in 1974. I'm hoping that was a good year at Criterion. And, the 1941 base number means it's the 941st DX8 made.

they really made that many?

Unless you bought your Dynamax new, you really don't get a grasp on how good they can be. IF they were all as horrible as some say how could they keep selling them for 10 years. I know Criterion too complaints seriously and took care of those customers.

In reality "MOST" of the Sad Sack stories come from someone buying a used one maz has passed through the hands of Lord knows how many people. All of those folks then repeat ALL are junk, there is even proof of my theory in the Articles section on this site where the Author ends his piece with the statement they are ALL Junk. This is after the stunning detective work of owning or looking through exactly ONE scope. Many a DX8 are still in the hands of their original owners and still in use. And I have looked through good to excellent examples. They did send out scopes they shouldn't have but many of the worst offenders were built after the Celestron Lawsuit, with much of the Companies cash assets going to the only people that really WON in that action, The Lawyers.

My kitchen table is about 4 feet in diamter, and my wife would kill me if I set up even a temporary optical bench there. Ain't gonna happen until I get the basement cleaned out! Of course, I have a friend with a Zygo- not everyone does.

This would fit on your kitchen table, and could involve vegetable oil (the flat).

You wouldn't even have to be a Mac person, but it would certainly help if you are...